Following through the links reveals that the IP has ended up on the Composite Blocking List due to a suspected Conficker infection (from whoever was on the IP previously; we’ve only started using this IP this morning). This is a fair reason to add it to the block list, however the CBL page also says:

“The CBL is intended to be used only on inbound email from the Internet.

If you are being blocked from IRC, Chat, web sites, web email interfaces (eg: you’re using Internet Explorer or Firefox to send email) or anything other than basic email with a mail reader like Exchange, Thunderbird etc, the provider of this service is using the CBL against our recommendations. Contact the provider and refer them to http://www.abuseat.org/tandc.html and refer them to item 2 and 7."

Since wiki != email this would appear to be a case of the CBL being misused. It’s not a major problem for me, but it’s worth bearing in mind since it does go against their T&C’s.